The present invention relates to a printhead, a printing apparatus comprising said printhead, and a print control method thereof.
An ink-jet printing apparatus which forms an image on a printing medium, e.g., paper, is configured with a printhead, which is mounted on a carriage that scans in a main-scanning direction and discharges ink, and conveys the printing medium by conveyance means. In the image forming operation, in synchronization with the printhead""s scanning operation in the main-scanning direction, the printhead discharges ink, thereby performing a printing operation. Thereafter, the printing medium is conveyed for a predetermined distance in a sub-scanning direction. Printing is performed by repeatedly executing the foregoing operation. The printhead of this type includes a plurality of nozzles. When the printhead is scanned in the main-scanning direction, ink is selectively discharged from respective nozzles, thereby printing an image.
In image printing, in a case where a large number of nozzles are simultaneously driven for ink discharge, a current that flows through the printhead is higher compared to a case where a small number of nozzles are simultaneously driven. Therefore, when a large number of nozzles are simultaneously driven for ink discharge, a voltage applied to the printhead drops due to the influence of contact resistances and wire resistances or the like. When such voltage drop occurs, heating elements (heaters) of the nozzles are not sufficiently heated, thus causing insufficient ink evaporation. As a result, it causes a problem in that ink is not appropriately discharged from respective nozzles.
In order to overcome such problem, the following measure may be considered. In a case where the number of nozzles simultaneously driven for ink discharge is large, the heating time-length for applying a voltage to electric resistances of the heating elements is set sufficiently long so that required electric energy is always supplied to the heating elements. In other words, conventional general ink-jet printers overcome the above-described problem by setting a longer heating time-length in a case where the number of nozzles simultaneously driven is large, and setting a shorter heating time-length in a case where the number of nozzles simultaneously driven is small.
In order to determine whether the number of nozzles simultaneously driven is large or small, the number of nozzles to be driven must be detected in advance of heating the heating elements, and the heating time-length must be calculated based on the number of nozzles to be driven. Such advance calculation function of the heating time-length is generally provided in an internal unit of a gate array circuit which generates print data to be sent to the printhead. In other words, at the time of sending print data to the printhead, the gate array circuit calculates the heating time in accordance with the print data and the number of nozzles to be driven simultaneously, and at the time of actual heating, the gate array circuit outputs a pulse signal having a pulsewidth corresponding to the calculated heating time (hereinafter referred to as a heat pulse) to the printhead, thereby controlling the ink discharge.
However, if a waveform of the heat pulse is distorted while the heat pulse is transmitted from the gate array circuit to the printhead mounted to the carriage, the above-described control of heating time cannot be accurately performed. In general, a gate array circuit is mounted to a control substrate fixed to the printer main unit. From the output pin of the substrate to the input pin of the printhead mounted on the carriage, the heat pulse must go through at least three connectors and at least one flexible cable. If an influence of contact resistances and wire resistances of the connectors or cables and an electric capacity of wires causes distortions in a rising edge or a trailing edge of the waveform of the heat pulse, accurate control of the heating time cannot be achieved.
The present invention has been proposed in view of the above conventional art, and has as its feature to provide a printhead which stores data related to a printhead""s driving time-length in an internal portion of the printhead so that respective printing elements of the printhead can be driven based on the data, and to provide a printing apparatus comprising said printhead, as well as a print control method thereof.
Another feature of the present invention is to provide a printhead which stores data related to a printhead""s driving time-length so that mere supplying of a driving start signal from an external unit of the printhead can realize driving of the printhead corresponding to the driving time-length, and to provide a printing apparatus comprising said printhead, as well as a print control method thereof.
Another feature of the present invention is to provide a recording head for recording by driving heating elements in accordance with recording data, comprising: a shift register adopted to serially receive the recording data and a signal for designating a time period of driving the heating elements via a signal line from a main body of an ink-jet apparatus; and recording means for recording using the recording data stored in the shift register and the signal for designating the time period of driving the heating elements.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.